JP2011064647A - Quality evaluation method of silica fume for high-strength concrete - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a quality evaluation method of a silica fume for a high-strength concrete which simply and intuitively evaluates the dispersibility of the silica fume in a premise for manufacturing the high-strength concrete. <P>SOLUTION: A sample slurry is manufactured by kneading the silica fume having a water-powder ratio of 350-450%, water and a water reducing agent of 3 wt.% or more and less than 5 wt.% relative to the silica fume. A viscosity of the sample slurry is measured by using a viscosity measuring instrument as an inexpensive and highly portable rotation viscometer. The dispersibility of the silica fume can be simply and intuitively evaluated in the premise for manufacturing the high-strength concrete. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for evaluating the quality of silica fume for high-strength concrete, and more specifically, the quality of silica fume for high-strength concrete capable of evaluating the dispersibility of silica fume added as an admixture that increases fluidity and strength to high-strength concrete. It relates to the evaluation method.

High-strength concrete usually increases strength development by decreasing the water cement ratio and increasing the unit cement amount. For this reason, the fluidity of concrete tends to deteriorate and workability tends to deteriorate, and measures have been taken, for example, by increasing the amount of addition of a high-performance water reducing agent. Moreover, since the amount of unit cement is large, the hydration heat generation amount is also increased, so that the durability of the structure after construction is lowered. Therefore, these problems are solved by adding silica fume to the low heat-generating cement mainly composed of C ₂ S (2CaO · SiO ₂ ).

  In general, silica fume is ultrafine particles having an average particle size of 0.1 μm or less, and primary particles are aggregated to exist as secondary particles (average particle size of about 20 μm). Therefore, when silica fume is mixed with cement or the like to produce concrete, the silica fume is dispersed up to the primary particles, which increases the fluidity of the concrete due to the micro filler effect and the close-packing effect, thereby increasing the strength. Be expected. Thereby, what is easy to disperse | distribute to a primary particle is desired for the silica fume used for high-strength concrete.

Therefore, conventionally, as a method for evaluating the dispersibility of particles of silica fume, by measuring the particle size distribution of silica fume using a laser diffraction type particle size distribution measuring apparatus that disperses silica fume using ultrasonic waves as an external force, the particle size distribution of 1 μm or less is measured. A method is known in which the silica fume dispersion degree is determined by measuring the proportion of silica fume having a particle size (for example, Patent Document 1).
Conventionally, as a high-strength concrete material comprising a cement composition, an inorganic admixture, an aggregate, a water reducing agent, and water, the cement composition has a belite content of 45 to 75% by mass in a clinker mineral composition, and an aluminate. The phase is 4.0% by mass or less, the specific surface area is 3000 to 4500 cm ² / g, the amount of SO ₃ is 1.5 to 4.5% by mass, and the proportion of hemihydrate gypsum is 80 mass with respect to the total amount of gypsum. % For a paste composed of 70 to 84 parts by mass of low heat Portland cement and 16 to 30 parts by mass of silica fume and water and a high-performance water reducing agent, A method for evaluating the quality of silica fume by the initial L flow velocity using an L flow tester is known (Patent Document 2).

Japanese Patent No. 3300993 JP 2007-119257 A

However, the silica fume evaluation method of Patent Document 1 requires special equipment such as an ultrasonic generator and a laser diffraction particle size distribution measuring device. As a result, it was necessary to perform the test in a test room or the like, not on the site where the silica fume was actually used.
Moreover, the evaluation of the dispersibility of the silica fume was easily influenced by other factors not related to the silica fume, such as the quality of cement described in Patent Document 2. Therefore, although it is an effective evaluation method experimentally, it was not suitable for confirming the quality of silica fume at the production site.

  Therefore, as a result of earnest research, the inventor found that the sample slurry obtained by kneading silica fume, a water reducing agent, and water was subjected to a depletion re-stabilization phenomenon that occurred after depletion and aggregation of silica fume as the amount of water reducing agent added increased. Pay attention. That is, when the water reducing agent is present in a very low concentration in the sample slurry, the silica fume exhibits an aggregating action due to the crosslinking formation of the water reducing agent. Thereafter, with the increase in the concentration of the water reducing agent (medium concentration), an adsorption layer of the water reducing agent is formed on the surface of the silica fume particles, and the stabilization of the silica fume is promoted by the steric repulsion effect between the adsorption layers (steric stabilization). However, if the concentration of the water reducing agent is further increased (slightly high concentration), the excessive non-adsorbed water reducing agent exerts a depleting aggregation effect as a free molecule and induces a gentle aggregation of silica fume. Furthermore, if the concentration of the water reducing agent is increased (high concentration), the water reducing agent also enters between the silica fume, impedes access between the silica fume particles and causes depletion re-stabilization.

  Using such depletion re-stabilization after depletion of silica fume, the viscosity of the sample slurry and the quality of the silica fume are judged. Specifically, first, a sample slurry is prepared by dispersing a predetermined amount of silica fume in water to which a water reducing agent (addition amount: 3% or more and less than 5%) is added. Next, the viscosity of the sample slurry is measured with a rotational viscometer that is cheaper and easier to transport than a laser diffraction particle size distribution analyzer. If the measurement result is 50 mPa · s or less, the proportion of silica fume of 1 μm or less is 30% or more, which is a criterion for determining good or bad with respect to the dispersibility of the silica fume. On the other hand, if it exceeds 50 mPa · s, the proportion of silica fume of 1 μm or less becomes less than 30%, and it is evaluated as defective silica fume. This measurement result correlates with the measurement result obtained by the conventional method employing the ultrasonic dispersion method. As a result, it was found that the dispersibility of silica fume can be easily and directly evaluated at the production site of high-strength concrete, and the present invention was completed.

  An object of the present invention is to provide a quality evaluation method for silica fume for high-strength concrete, which can easily and directly evaluate the dispersibility of silica fume at the production site of high-strength concrete.

  The invention according to claim 1 is to prepare a sample slurry by kneading a silica fume having a water powder ratio of 350 to 450%, water, and a water reducing agent of 3 wt% or more and less than 5 wt% with respect to the silica fume. The obtained sample slurry is put into a measuring container, and the viscosity is measured with a rotational viscometer. If the measured viscosity value is 50 mPa · s or less, it is judged as good, and if it exceeds 50 mPa · s, it is regarded as defective. This is a quality evaluation method for silica fume for high strength concrete.

According to the first aspect of the present invention, silica fume, water and a water reducing agent are kneaded to prepare a sample slurry. At this time, the water powder ratio of silica fume and water is 350 to 450%, and the amount of water reducing agent added is 3% by weight or more and less than 5% by weight with respect to the silica fume.
Thereafter, the sample slurry is put in a measurement container, and the viscosity is measured with a rotational viscometer. As a result, if the measured value is 50 mPa · s or less, the ratio of silica fume of 1 μm or less is 30% or more, and it is evaluated as a good silica fume (graph in FIG. 2). On the other hand, if it exceeds 50 mPa · s, the proportion of silica fume of 1 μm or less becomes less than 30%, and it is evaluated as a defective silica fume. It is clear that this evaluation method is correct from the point of correlation with the measurement results obtained by the conventional method employing the ultrasonic dispersion method (graphs of FIGS. 1 and 3, Tables 1 to 3 (brand names of SF1 to SF6, etc.) See Table 4)). Table 1 is data obtained by digitizing the graph of FIG. 1, Table 2 is data obtained by digitizing the graph of FIG. 2, and Table 3 is data obtained by digitizing the graph of FIG.

  In this way, a sample slurry is prepared by kneading silica fume having a water powder ratio of 350 to 450%, water, and a water reducing agent of 3 wt% or more and less than 5 wt% with respect to the silica fume. The measuring instrument is configured to measure the viscosity of the sample slurry using a rotational viscometer that is cheaper and more portable than conventional laser diffraction particle size distribution analyzers. It can be easily and directly evaluated at a manufacturing site of high-strength concrete that is not a laboratory.

High-strength _concrete, C 2 S and (2CaO · SiO ₂₎ in the cement as a main component, silica fume, to produce a high-strength concrete cementitious composition by mixing 4-21 wt% with respect to the cement, then, The cement composition for high-strength concrete, coarse aggregate, fine aggregate, water, and a water reducing agent are put into a mixer at a predetermined ratio, and these are kneaded. In some cases, fine limestone powder may be used instead of silica fume.
As the brand of silica fume, for example, Egypt (Efaco) Lot; 2508, Egypt (Efaco) Lot; 3308, Egypt (Efaco) Lot; 4208, Egypt (Efaco) Lot; 3507, Egypt (Efaco) Lot; 0707, Egypt ( Efaco) Lot: 2408, Jiangxi Yuyuan Si Industry Co., Ltd. (China), China SiO ₂ = 95% (Shinko Corporation), Selma Factory SF of America Grove Company, etc. These qualities are shown in Table 4. In Table 4, the dispersibility value is a value measured by a laser diffraction particle size distribution measuring apparatus.

The content of SiO ₂ in silica fume is as high as 95% or more for metal silicon, but 85 to 95% for ferrosilicon. If it is less than 85%, the quality standard of JIS A 6207 “silica fume for concrete” cannot be satisfied, and a pozzolanic reaction due to SiO ₂ cannot be expected. The preferable content of SiO ₂ in silica fume is 90% or more. If it is this range, the more suitable effect that the pozzolanic activity with Ca (OH) ₂ which exists in mortar and concrete will improve is acquired.
If the average particle size of the silica fume exceeds 1.0 μm, the fluidity of the fresh concrete mixed with the silica fume decreases, and the characteristics of the silica fume such as a decrease in the close-packing effect or a decrease in the pozzolanic activity are decreased. The preferable average particle diameter of the silica fume is 0.1 to 0.3 μm. If it is this range, the more suitable effect of the improvement of the fluidity of fresh concrete and the improvement of the compressive strength by the close-packing effect will be acquired.

If the water powder ratio of silica fume and water is less than 350%, the slurry viscosity becomes high regardless of the dispersibility of the silica fume. On the other hand, if it exceeds 450%, the slurry viscosity becomes low regardless of the dispersibility of the silica fume. A preferable water powder ratio of silica fume and water is 390 to 410%. If it is this range, according to the dispersibility of a silica fume, the more suitable effect that the difference of slurry viscosity will become clear will be acquired.
For example, tap water can be used as the water.

As the water reducing agent, for example, a high performance water reducing agent (Tupole SSP-104 manufactured by Takemoto Yushi Co., Ltd. which is a polycarboxylic acid ether compound) can be employed. In addition, a high-performance AE water reducing agent may be used.
When the amount of the water reducing agent added to the silica fume is less than 3% by weight, the slurry viscosity is high even if the dispersibility of the silica fume is good. Moreover, if it is 5 weight% or more, even if the dispersibility of a silica fume is bad, slurry viscosity will become low. The preferred amount of water reducing agent added to silica fume is 3.0 to 4.0% by weight. If it is this range, the more suitable effect that the difference of the viscosity of a slurry will become clear according to the dispersibility of a silica fume is acquired.

Kneading with a mixer can be employed for kneading silica fume, water, and water reducing agent.
For kneading, for example, any two materials of silica fume, water, and water reducing agent may be kneaded in advance, and then the remaining one material may be additionally added and kneaded again. In addition, these three may be charged simultaneously and kneaded.

A rotational viscometer is a viscometer utilizing the fact that when an object (rotor) such as a cylinder, a disk, or a sphere is rotated in a fluid, the object receives torque due to the viscous resistance of the fluid.
As a type of rotational viscometer, for example, a rotational viscometer for low viscosity (TV-10M type) manufactured by Toki Sangyo Co., Ltd. or a rotational viscometer for medium / high viscosity (TV-10 H type) is adopted. be able to.
Viscosity measurement conditions using a rotational viscometer are as follows: the temperature of the sample slurry is 0 to 40 ° C. (preferably 18 ° C. to 25 ° C.), the rotation speed of the rotor is 0.3 to 60 rpm, and the medium to high In the case of a viscosity type apparatus, it is 2 to 100 rpm, and a relative viscosity of 10 to 2000 mPa · s can be measured by selecting an appropriate model and rotor according to the viscosity of the sample.

  If the measured value of the sample slurry by a rotational viscometer is 50 mPa · s or less, the proportion of particles having a size of 1 μm or less, which indicates good dispersibility of silica fume, is 30% or more (graph in FIG. 2). Therefore, the silica fume is determined as a non-defective product. On the other hand, if the measured value exceeds 50 mPa · s, the proportion of particles having a size of 1 μm or less, which indicates good dispersibility of silica fume, is less than 30%, and the silica fume is determined to be defective.

  In the invention described in claim 2, a mixer having a stirring blade is used for kneading the silica fume, water and a water reducing agent, and at the time of kneading, the stirring blade is rotated at 5000 to 12000 rpm and stirred. 1 is a method for evaluating the quality of silica fume for high-strength concrete according to 1.

  According to the second aspect of the present invention, the material of the sample slurry is kneaded by putting silica fume, water, and a water reducing agent into the container of the mixer and rotating the stirring blade at 5000 to 12000 rpm and stirring. Thereby, the silica fume which exists as a secondary particle can be disperse | distributed to a primary particle, and the component of a water reducing agent can be effectively contacted to the particle | grain surface of a silica fume.

  When the rotation speed of the stirring blade is less than 5000 rpm, the cohesive force of the secondary particles is strong, so that the silica fume particles are not dispersed. Moreover, since it will exceed the capability of a commercially available mixer if it exceeds 12000 rpm, a special stirrer is required. A preferable rotation speed of the stirring blade is 6000 to 10,000 rpm. If it is this range, the dispersive force given to a silica fume particle | grain will become most efficient, and the more suitable effect that a secondary particle will be easy to disperse | distribute comparatively easily will be acquired.

  Invention of Claim 3 is the quality evaluation method of the silica fume for high-strength concrete of Claim 2 whose kneading time of a silica fume, water, and a water reducing agent is 50 to 70 second.

  According to the third aspect of the present invention, since the mixing time of the silica fume, water, and water reducing agent by the mixer is 50 to 70 seconds at 5000 to 12000 rpm with the rotation of the stirring blade, the dispersibility of the silica fume is improved. Accordingly, the difference in viscosity of the slurry becomes clear.

  If the kneading time of silica fume, water and water reducing agent is less than 50 seconds, the silica fume particles cannot be dispersed to the primary particles, and the viscosity becomes high. Moreover, if it exceeds 70 seconds, the silica fume particle | grains once disperse | distributed will raise | generate agglomeration, and a viscosity will become high. A preferable kneading time is 55 to 65 seconds. If it is this range, the difference of the viscosity of a slurry will become clear according to the dispersibility of a silica fume.

  According to the first aspect of the present invention, first, a sample slurry is prepared by kneading a silica fume having a water powder ratio of 350 to 450%, water, and a water reducing agent of 3 wt% or more and less than 5 wt% with respect to the silica fume. Is made. After that, the viscosity of the sample slurry can be measured using a rotary viscometer that is inexpensive and highly portable, and does not require an expensive, large, and special measuring device like a conventional laser diffraction particle size distribution measuring device. taking measurement. As a result, with respect to the quality of silica fume used for the production of high-strength concrete, in addition to the performance defined by JIS, it is possible to evaluate the dispersibility involved in improving the fluidity of concrete and increasing the strength. Moreover, the dispersibility of the silica fume can be easily and directly evaluated at a production site of high-strength concrete that is not a specific laboratory.

  According to the second aspect of the invention, at the time of kneading, the silica fume, water, and water reducing agent charged in the mixer are kneaded by rotating the stirring blades at 5000 to 12000 rpm. Equivalent external force can be applied, and silica fume particles can be dispersed to primary particles.

  According to the invention described in claim 3, the kneading time of the silica fume, water, and water reducing agent by the mixer is set to 50 to 70 seconds at 5000 to 12000 rpm for the stirring blade, so that the time sufficient to disperse the silica fume particles. And an appropriate time that does not cause re-aggregation.

It is a graph which shows the relationship between the addition amount of the water reducing agent according to brand of silica fume, and the viscosity of a sample slurry. It is a graph which shows the relationship between the dispersibility of a silica fume and the viscosity of a sample slurry. It is a graph which shows the relationship between the addition amount of the water reducing agent of a silica fume, and the viscosity of a sample slurry. It is a graph which shows the relationship between the addition amount of the water reducing agent according to the brand of silica fume, and the viscosity of a sample slurry in the quality evaluation method of the silica fume for high-strength concrete which concerns on the Example of this invention. It is a graph which shows the relationship between the water powder ratio according to the brand of the silica fume in the quality evaluation method of the silica fume for high-strength concrete which concerns on the Example of this invention, and the viscosity of a sample slurry. It is a graph which shows the relationship between the kneading | mixing time of the sample slurry according to the brand of the silica fume in the quality evaluation method of the silica fume for high-strength concrete which concerns on the Example of this invention, and the viscosity of a sample slurry. It is a graph which shows the relationship between the rotation speed of the stirring blade mounted in the mixer according to the brand of the silica fume in the quality evaluation method of the silica fume for high-strength concrete which concerns on the Example of this invention, and the viscosity of a sample slurry.

  Examples of the present invention will be specifically described below. However, the present invention is not limited to this.

(1) Materials Used The materials used in the present invention are shown in Table 5 below.

  Note that the high-performance water reducing agent SSP-104 in Table 5 is an anionic polymer surfactant mainly composed of a polycarboxylic acid-based graft copolymer.

(2) Production of sample slurry (silica fume slurry) Commercially available high-speed stirring of 100 g of silica fume, a water reducing agent and 400 g of water (of which 0 to 10 g of water reducing agent) is carried out for each of the six types of silica fume (SF1 to SF6) shown in Table 5. The sample slurry was put into a mixer and kneaded by rotating the stirring blade at a high speed of 8000 rpm for 60 seconds to prepare each sample slurry.

[Quality (dispersibility) evaluation test by brand of silica fume]
Next, six kinds of sample slurries prepared according to the method for producing the sample slurry (2) were transferred to a measuring container for each brand, and their viscosities were measured with a rotational viscometer.
In a test room controlled at a room temperature of 20 ± 2 ° C. and a relative humidity of 85% RH or higher, the temperature of water used for preparing the slurry was 20 ± 1 ° C., and the temperature of silica fume was 20 ± 3 ° C.
If the viscosity of the sample slurry is 100 mPa · s or less, use a TV-10M type viscometer. If the viscosity of the sample slurry is less than 100 mPa · s, use the TV-10H type to measure the viscosity of the sample slurry. did.
The measurement time with the viscometer was 20 seconds per time, and each sample was measured three times, and the average value was taken as the measured value. A 500 ml poly beaker was used as a measurement container.
The results are shown in the graph of FIG.

  As is apparent from the graph of FIG. 4 and Table 6, SF1 to SF4, which are regarded as non-defective products by the conventional laser diffraction particle size distribution analyzer, have a viscosity of 3% or more and less than 5%. At 50 mPa · s or less, the dispersibility was such that the proportion of particles of 1 μm or less for which silica fume was good was 30% or more (graph in FIG. 2). On the other hand, defective SF5 and SF6 had a viscosity exceeding 50 mPa · s, and the dispersibility was such that the proportion of particles of 1 μm or less was less than 30%. That is, silica fume exceeding 50 mPa · s is evaluated as silica fume (granular) having extremely poor dispersibility or a large particle size, and there is a correlation between the evaluation method of the example and the evaluation method by the conventional method. It was proved.

  Here, with reference to the graph of FIG. 5 and Table 7, the result of investigating the change in the dispersibility of silica fume (SF3, SF4, SF6) due to the difference in the water powder ratio between silica fume and water will be reported. Specifically, the viscosity of the sample slurry when the water powder ratio of silica fume (constant at 100 g) and water is varied from 300 to 500% is shown. Other than that, the test was performed under the same conditions as in the above-described Examples.

  As is apparent from the graph of FIG. 5 and Table 7, when the water powder ratio is 350 to 450%, the viscosity of the sample slurry is 50 mPa · s or less, and the proportion of particles of 1 μm or less that makes silica fume good is 30%. That was all.

  Next, with reference to the graph of FIG. 6 and Table 8, the result of investigating the change in the dispersibility of silica fume (SF3, SF4, SF6) due to the difference in the kneading time of the sample slurry by the stirring blade will be reported. Specifically, the viscosity of the sample slurry when the kneading time is varied from 50 to 70 seconds is shown. The other conditions were tested under the same conditions as in the above-described example.

  As is apparent from the graph of FIG. 6 and Table 8, when the kneading time of the sample slurry is 50 to 70 seconds, the viscosity of the sample slurry is 50 mPa · s or less, and the proportion of particles of 1 μm or less that makes silica fume good is 30. % Or more.

  Next, referring to the graph of FIG. 7 and Table 9, the results of examining the change in the dispersibility of silica fume (SF3, SF4, SF6) due to the difference in the rotation speed of the stirring blades mounted on the mixer will be reported. Other than that, the test was performed under the same conditions as in the above-described Examples.

  As apparent from the graph of FIG. 7 and Table 9, when the rotation speed of the stirring blade is 8000 rpm (mixer A), the rotation speed is 139 rpm (mixer B), and the rotation speed is 500 rpm (mixer C), the rotation speed Only when the sample slurry was 8000 rpm, the viscosity of the sample slurry was 50 mPa · s or less, and the proportion of particles of 1 μm or less considered good for silica fume was 30% or more.

  The present invention is useful for evaluating the dispersibility of silica fume added to high-performance and high-quality shotcrete or high-strength concrete for high-rise buildings.

Claims (3)

A sample slurry is prepared by putting a silica fume having a water powder ratio of 350 to 450%, water, and a water reducing agent having a water content of 3 wt% or more and less than 5 wt% with respect to the silica fume into a mixer and kneading.
Put the obtained sample slurry in a measurement container, measure the viscosity with a rotational viscometer,
A method for evaluating the quality of silica fume for high-strength concrete, when the measured viscosity value is 50 mPa · s or less, which is a non-defective product, and when it exceeds 50 mPa · s, a defective product. A mixer having a stirring blade is used for kneading the silica fume, water and a water reducing agent,
The method for evaluating the quality of silica fume for high-strength concrete according to claim 1, wherein the stirring blade is stirred by rotating the stirring blade at 5000 to 12000 rpm.   The method for evaluating the quality of silica fume for high-strength concrete according to claim 2, wherein the kneading time of silica fume, water and water reducing agent is 50 to 70 seconds.

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